Those battleground state polls that paint such a grim picture of Donald Trump's prospects against Hillary Clinton? Most Republican insiders don't believe they're accurately capturing Trump’s true level of support.

That’s according to the POLITICO Caucus — a panel of activists, strategists and operatives in 11 key battleground states. More than seven-in-10 GOP insiders, 71 percent, say the polls understate Trump’s support because voters don’t want to admit to pollsters that they are backing the controversial Republican nominee.

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With Trump falling behind in the majority of swing states, an overwhelming polling error may represent his best hope to win next month — and even that may not be enough. At the same time GOP insiders say there are “shy Trump” voters out there who aren't showing up in the polls, a 59-percent majority still say Clinton would win their state if the election were held today.

“I'm not sure how big a factor it is, but there is definitely a ‘Bradley effect’ going on out there,” said a Virginia Republican, referring to the African-American mayor of Los Angeles who led in polls but lost unexpectedly in the 1982 California gubernatorial race. “I personally know many Republicans that won't admit that they are voting for Trump. I don't like admitting it myself. It won't matter if Hillary is up more than 5 points, but we might be in for a surprise if Hillary's lead is less than 5 points on Election Day.”

A Michigan Republican — who, like all insiders, completed the survey anonymously —added that Trump voters are reticent to admit it publicly: “Anecdotally, that's clearly the case in barber-shop conversations.”

A number of Republicans said that while they believe the polls are underestimating Trump, his deficit is too large for it to matter.

“He'll outperform the polls but still won't win,” a Pennsylvania Republican said.

“This form of survey bias is a common but marginal factor in many polls,” an Ohio Republican added.

For other Republicans, the “shy Trump” effect that might be deflating Trump’s support is less an issue than other sources of bias in the polls.

“I also believe that by polling likely voters rather than registered voters, polls are missing a lot of where Trump's support lies,” an Iowa Republican said.

The phenomenon known as social desirability bias “may be part of it,” a Nevada Republican said. “I also think that the pollsters have not accounted for the uniqueness of this election and are not necessarily asking the right questions of the correct samples. Finally, many of the polls are deliberately slanted to suit the media's political agenda. Taken all together, it’s almost impossible to know who is leading at this point.”

Some cited the energy of Trump supporters to suggest his backers are unforthcoming with pollsters.

“I see a lot of Trump signs on people's lawns, plus a lot of anti-Clinton signs,” said a New Hampshire Republican.

But for a minority of Republicans, 29 percent, those hoping for a secret Trump vote to emerge on Election Day will be disappointed.

“We did not see this in the primaries. There is no basis [for it],” a Michigan Republican said. “I think there is just as much pressure on Republicans to say you're going to vote for him when you have no intention [to do so].”

“Does anyone really care whether or not a survey-taker disapproves of their choice?” a North Carolina Republican asked. “Besides, Trump doesn’t always fare worse in live-caller polls. The IBD/TIPP poll, which has been among the handful of outlier polls more positive to Trump, is after all a live-caller poll. The truth is that Trump's support is not substantially different in live-caller polls versus IVR and internet panels. Both types of polls have outliers, but the difference is not a significant one.”

Added a Colorado Republican: “In 2012 people said the polls were wrong because voters didn't want to sound like racists for not voting for President Obama. Polls weren't wrong. People on the losing side of the polls always invent a reason for it.”

A Florida Democrat called it a “ludicrous claim by someone who is losing. As someone who has been on unsuccessful campaigns I know what it's like to throw out every excuse in the book to keep supporters engaged.”

But some Democrats, drawing from experiences in their states, are concerned that these voters do exist — and they could be more of a factor in a closer race.

“Former [Philadelphia] Mayor Frank Rizzo always outperformed his polling numbers because voters would not admit their true intentions,” a Pennsylvania Democrat said. “There is no doubt there is a sense of embarrassment and isolation for the Trump voter who is educated and lives in Philadelphia or its suburbs. And I would think the phenomena holds true in similar markets. I think this also holds true with African-American voters. There is a hidden vote for him above what the polling shows. But a hidden vote in either scenario is a few points in that subset, not enough to get him to the promised land.”

“That is what we call in Virginia the ‘Wilder factor,’” a Democrat there added. “Voters did not want to admit that they were not going to vote for the first African American for Governor in 1989, thus making the race close. I think there is some of that, but not in record numbers.”

Other Democrats insisted that the polls are under-representing Clinton supporters, not Trump voters.

“I think the polls are just as likely to underestimate Hispanic support and enthusiasm as they are to underestimate angry white guys,” a Florida Democrat said.

And an Iowa Democrat suggested: “I think polls underestimate Clinton's strength because of the married women who tell their husbands they are for Trump to keep the peace.”

GOP insiders: Trump choking on Obamacare opportunity

The Obama administration’s announcement this week that premiums would rise next year for individual health-insurance plans available on the exchanges vaulted the 2010 health-care law back into the electoral debate.

But GOP swing-state insiders say Trump has failed to capitalize on the lingering dissatisfaction with Obamacare, particularly with Republicans and the persuadable swing voters Trump needs to make the race more competitive.

Only 28 percent said Trump is doing a good job attacking Clinton on the Obamacare premium increases, while 72 percent said he isn’t doing a good job.

Many of those dissatisfied with Trump’s response cited his Wednesday-morning event in Washington: a ribbon-cutting at the new Trump hotel on Pennsylvania Avenue.

“Donald Trump and Republicans were just handed a lifeline with the Obamacare premium increases,” a Colorado Republican said. “Instead of using it to help his own campaign and down-ticket Republicans, Trump has decided to focus his time talking about Trump Hotel.”

“When you are spending time opening a hotel you are wasting a golden opportunity to strike fear in the hearts of Democrats everywhere,” a Florida Republican added.

Other Republicans complained about Trump’s lack of discipline overall, which they say undermines his message.

“If the GOP had a candidate who could effectively prosecute the case instead of getting distracted by sideshows, then this could be a huge deal in this election,” an Ohio Republican said.

Some Republicans said that while the premium increases could raise an argument for most GOP candidates, Trump has struggled to make cogent critiques on more complex issues during the campaign.

“Like everything else, he doesn't take the time to understand what is really happening and shows no real insight into the problem nor does he propose any rational solutions,” a New Hampshire Republican said.

“He doesn't understand policy, he doesn't care about policy, and he's not a conservative,” a Virginia Republican added. “So you just handed a one-year-old an iPhone. He'll try to push the buttons but not in any manner that makes sense or works.”

Among the minority of GOP insiders who said Trump was doing a good job hitting Clinton on the issue, some couched their praise.

One Ohio Republican said Trump was doing “as well as can be expected for a guy who has voiced support for various forms of single-payer health care.” A New Hampshire Republican wondered whether Trump “can … consistently stay focused on that message or will he wander off into issues that don't matter.”

A Virginia Republican said the issue could still help Trump because “anything that makes people think about [Clinton] helps Trump and hurts [Clinton].”

Meanwhile, Democratic insiders mostly said Clinton was doing a good job dealing with dissatisfaction with Obamacare: 78 percent to 22 percent.

“She has repeatedly said here that there are things that need to be fixed, and people here at least understand she had nothing to do with this version of it,” a New Hampshire Democrat said.

These are the members of The POLITICO Caucus, not all of whom participated in this survey: